1. Field of the Invention
The present invention relates to structures for high-frequency semiconductor devices on which high-frequency semiconductor elements, control integrated circuit elements, and surrounding circuits are mounted, and in particular to packaging structures thereof.
2. Description of the Related Art
There is an increasing demand for high-frequency semiconductor devices employed primarily in mobile communications equipment, such as portable telephones, as xe2x80x9call-in-onexe2x80x9d RF modules with receiving and transmitting systems formed into a single unit. According to such situation, a need has arisen for a reduction in packaging size, under the condition that the number of semiconductor elements and chip components that are mounted increases due to the provision of high-frequency semiconductor elements, control integrated circuit elements and surrounding circuitry in order to incorporate receiving and transmitting systems into a single unit.
A conventional example of a high-frequency semiconductor device is described with reference to FIG. 10. In FIG. 10, numeral 1 denotes a semiconductor element of a chip form such as a transistor and 2 denotes a ceramic multilayer substrate. Numeral 3 denotes chip components such as chip resistors, chip capacitors, and chip inductors. Numeral 4 denotes bottom electrodes, 5 denotes metal wires, 6 denotes potting resin, and 7 denotes a metal cap.
Component mounting lands for mounting the semiconductor element 1 and the chip components 3 and an electrode wiring pattern (not shown) are formed on the surface of the ceramic multilayer substrate 2 through screen printing or metal thin film etching, for example. The semiconductor element 1 is die bonded to the component mounting land portion on the ceramic multilayer substrate 2, and connected to the electrode wiring pattern that is formed on the surface of the ceramic multilayer substrate 2 by the metal wires 5. The semiconductor element 1 and the metal wires 5 are covered by the potting resin 6. The chip components 3 are mounted to predetermined locations by soldering. The metal cap 7, which forms the packaging, is attached to the ceramic multilayer substrate 2. The electrode wiring pattern on the surface of the ceramic multilayer substrate 2 is connected electrically to the bottom electrodes 4 via through holes, which are not shown, that pass through the ceramic multilayer substrate 2.
However, with structures where semiconductor elements and chip components are simply mounted onto the ceramic multilayer substrate 2, as is the case with the conventional high-frequency semiconductor device described above, the desired reduction in the packaging size cannot be met sufficiently as the number of installed components increases.
Also, the semiconductor chip provided on the ceramic multilayer substrate is a heat-generating element such as a power amplifier, and thus all the heat generated from the semiconductor chip is transferred to the bottom portion via the ceramic multilayer substrate and released from the bottom portion electrodes. However, the ceramic multilayer substrate has a high thermal resistance. This led to the problem of not enough heat being released from the semiconductor chip, which consumes a large amount of power, and the semiconductor chip becoming hot.
It is an object of the present invention to provide a high-frequency semiconductor device in which receiving and transmitting systems including active elements such as semiconductor elements like power amplifiers and switches or semiconductor elements for control, and passive components such as resistors, capacitors, inductors, and filters, are mounted as a single unit in a layered substrate, so as to improve electrical properties by reducing impedance due to the reduction in the wiring length, reducing the floating capacity, and improving anti-noise properties, and to provide a smaller size device with improved heat release properties.
A high-frequency semiconductor device of the present embodiment is provided with a ceramic substrate, an element group including semiconductor elements and passive components mounted onto a bottom portion of the ceramic substrate, and a composite resin material layer formed on the bottom portion of the ceramic substrate so as to bury the element group. The composite resin material layer is formed of a composite resin material including an epoxy resin and an inorganic filler material, and has a flat bottom surface on which electrodes for connecting to the outside are formed.
With this configuration, the semiconductor elements and passive components are mounted on the bottom portion of the ceramic substrate, so that the bottom surface of the substrate can be utilized as the mounting area and the mounting density can be increased. Also, by burying the element group in the composite resin material layer, an increase in reliability, such as mechanical resistance and resistance against moisture, can be achieved. Moreover, by making the bottom surface of the composite resin material layer flat and providing the electrodes for connecting to the outside, the product is easily transported and handled, and the ability to mount the high-frequency semiconductor device as a module is improved.
It is preferable that the semiconductor elements are mounted by flip-chip connection. Thus, a drop in impedance due to the reduction in wiring length, a reduction in the floating capacity, an increase in the mounting density, and reduction in the height of the packaging can be achieved.
The high-frequency semiconductor device mentioned above can be given a structure where interlayer connector structures are formed in the composite resin material layer, the interlayer connector structures being filled with a high thermal conductivity resin material having thermal conductivity higher than that of the epoxy resin, the electrodes for connecting to the outside include a ground electrode that functions as a heat release electrode, and the surface of the semiconductor element is connected to the ground electrode via the interlayer connector structures. Thus, heat generated by the semiconductor elements, which are heat-generating elements such as power amplifiers and mounted by flip-chip connection, can be adequately released from the electrodes for connecting to the outside via the interlayer connector structures provided in a single or a plurality of locations.
Another high-frequency semiconductor device of the present invention is provided with a first ceramic substrate having a circuit pattern, a second ceramic substrate on which semiconductor elements are mounted, and a composite resin material layer that buries the semiconductor elements and is provided between the first ceramic substrate and the second ceramic substrate. The composite resin material layer is formed by a composite resin material including an epoxy resin and an inorganic filler material, interlayer connector structures in which a conducting resin material has been filled are formed in the composite resin material layer, and the circuit pattern of the first ceramic substrate and a circuit pattern of the second ceramic substrate are electrically connected via the interlayer connector structures.
According to this configuration, the first ceramic substrate and the second ceramic substrate are employed according to the electrical, thermal, and mechanical properties that are required, and are deposited with the composite resin layer interposed between them, so that a small size substrate packaging can be formed. Even if the linear expansion coefficients of the first ceramic substrate and the second ceramic substrate are different, a highly reliable packaging that absorbs this difference can be provided, because the composite resin layer is interposed between the substrates. In addition to the fact that semiconductor elements and passive component can be mounted between the first ceramic substrate and the second ceramic substrate, it is also possible to mount components on the upper surface of the first substrate, and thus the overall mounting density of the product can be increased. Moreover, by burying the semiconductor elements, for example, with the composite resin, reliability such as mechanical resistance and resistance against moisture can be increased.
In this configuration, it is preferable that the semiconductor elements provided on the second ceramic substrate have been mounted by flip-chip connection. Thus, the thickness of the composite resin material layer between the first ceramic substrate and the second ceramic substrate can be reduced. Also, a drop in impedance due to the reduction in wiring length, a reduction in the floating capacity, an increase in the mounting density, and a reduction in the packaging height can be achieved.
Additionally, it is possible to adopt a configuration in which at least one of the semiconductor elements provided on the second ceramic substrate is connected by metal wires. Thus, those elements of the semiconductor elements that are mounted onto the second ceramic substrate for which the release of heat is required can be adhered by a high conductivity adhesive agent and connected to the substrate by the metal wire, so that heat can be dissipated from those elements directly to the second ceramic substrate. This configuration is particularly effective when a large amount of heat is generated by the semiconductor elements.
In this configuration, the surroundings of the semiconductor elements provided on the second ceramic substrate and connected by the metal wire can be sealed by a liquid epoxy resin. Thus, stress that is applied to the semiconductor elements and the metal wire when the first ceramic substrate and the second ceramic substrate are adhered by the composite resin material can be alleviated, so that defects such as the wire falling over or being disconnected can be eliminated, and the assembly yield can be increased. Moreover, the epoxy resin that seals the semiconductor elements can be employed as a spacer for the first ceramic substrate and the second ceramic substrate, so that the gap between the two substrates can be adjusted.
A further high-frequency semiconductor device according to the present invention is provided with a ceramic substrate having a cavity portion in its bottom portion, an element group including semiconductor elements and passive components mounted to the bottom portion of the cavity portion, a composite resin material layer formed so as to bury the element group in the cavity portion, and electrodes for connecting to the outside that are formed on a bottom portion of the ceramic substrate other than at the cavity portion. The composite resin material layer is formed by a composite resin material including an epoxy resin and an inorganic filler material, and a bottom portion of the composite resin material layer is flat in shape.
As in the configuration mentioned above, this configuration achieves an increase in the mounting density, an increase in device reliability such as in the mechanical resistance and in the resistance against moisture, and an increase in mountability. Additionally, the composite resin material layer can easily be formed by filling a composite resin material into the cavity portion.